Temperature- and solvent-controlled dimensionality in a zinc 6-(1H-benzoimidazol-2-yl)pyridinecarboxylate system

Several 0D, 1D, and 3D metal-organic hybrid frameworks of Zn-II have been synthesized by using the asymmetric ligand 6-(1H-benzoimidazol-2-yl)pyridinecarboxylic acid (HL) with control of the temperature and solvent in a solvothermal synthesis technique. In DMF, the structure at room temperature confirms that the resulting compound Zn(L)(2)center dot 2(H2O) (1) is the 0D mononuclear structure, above similar to 80 degrees C, C-N bond cleavage of partial DMF molecules induces the formation of the 1D chain-like compound {[Zn(L)(HCOO)]center dot 2(H2O)}(n) (2), but on warming up to 120 and 160 degrees C, due to the decomposition of a large number of DMF molecules, the same reaction, respectively, gives two 3D metal-organic coordination polymers with 3D channels reported previously {[Zn(HCOO)(3)](-)center dot[H2N(CH3)(2)](+)}(n) (3) and [Zn(HCOO)(2)](n) (4), in which the 3D channels of 3 contain guest [H2N(CH3)(2)](+) Motifs, while at high temperature the 3D channels of 4 are an open stable system without any guest molecules. Replacing DMF in the above reaction by ethanol or acetonitrile, only 0D compound 1 is obtained in the range from room temperature to 160 degrees C. However, the same reaction in DMSO provides a 1D wave-like compound {[Zn(L)(DMSO)]center dot(ClO4)center dot H2O}(n) (5), in which the solvent DMSO molecule coordinates to the central metal Zn-II ion. Furthermore, in three new complexes 1, 2 and 5, through pi center dot center dot center dot pi stacking and hydrogen bonding interactions, 3D supramolecular networks are assembled. It is worth noting that the existence of the twelve-membered cyclic water-perchlorate dimers [(ClO4)center dot center dot center dot(H2O)](2)(2-) with chair-conformation in the solid state of 5 not only increases the stability of the supramolecular structure, but also results in a stronger fluorescence signal compared with ligand HL, 1 and 2.